This invention relates to an antihydroplaning system for a motor vehicle in which the start of a hydroplaning of the motor vehicle tires on sheets of water on roads because of a lack of contact with the road (slip) is recognized electronically.
So-called slip control systems (ASR's) are known which determine an adhesion coefficient dependent on the condition of the road surface, and a relevant slip threshold as a function thereof. See, for example, German Patent Document DE-OS 37 40 433 A1.
Arrangements for eliminating the hydroplaning effect caused by water puddles on the road, for example by breaking up the water film by means of a gas jet arriving before the tare, are disclosed in the German Patent Documents 22 39 022 A1, DE-OS 26 00 787 A1, and DE-OS 34 17 048 A1. In particular, these devices involve the use of a compressed-air jet.
Japanese Patent Document JP 1-226 403 (A) in: Patent Abstracts of Japan, Section M. Vol. 13 (1989), No. 552 (M-903), discloses a device for improving wheel adhesion in which friction-promoting means provided in front of the wheels of the vehicle are controlled by a computer in response to a logical linking of sensor signals for the detection of the rotational wheel speed (in order to recognize the slip of the wheels), and additional sensors (for example, for the driving speed, the actuating of the brake, the rotational engine speed), as well as by means of electronic devices for the signal analysis and the evaluation of the signals which are supplied by the individual sensors to the evaluating device of the computer.
Modern road vehicles, particularly passenger cars, routinely include the following vehicle-borne installations:
a computer, PA0 vehicle electronic system with its own power supply; PA0 a hydraulic system and devices for controlling it, particularly by means of the electronic system; PA0 an antilock system, PA0 a slip control system, the two latter control systems comprising at least one and preferably several sensors for the detection of rotational wheel speeds. PA0 at least one ambient temperature sensor, either for the purpose of the engine/fuel control or for the purpose of air conditioning the vehicle interior. PA0 The water layer in front of the tire is broken up by means of a mass jet of gas, liquid or particles. PA0 The steering booster/power steering is disabled, thus largely avoiding a dangerous locking of the wheels. PA0 The fuel supply, is throttled, initiating a moderate vehicle deceleration and therefore a reduction of the danger potential. PA0 The water layer is displaced by mechanical devices.
In addition, the system on which the present invention is based also comprises a device, known per se, for aiming a mass jet in front of the wheels of the vehicle.
It is an object of the invention generally to reduce the danger of accidents, and in particular to provide a system which is capable of reliably detecting and recognizing the above-described hydroplaning effect by means of electronic recognition devices, and initiating measures to combat and eliminate it.
This object is achieved by the antihydroplaning system according to the invention in which, unlike present antilock system (ABS) and slip control systems (wherein only the rotational wheel speed is evaluated as the main signal), the outputs of a variety of sensors are analyzed to recognize clearly whether there is the danger of hydroplaning (that is, the start of a hydroplaning by the tires over sheets of water). Where a danger of hydroplaning is determined to exist, the invention triggers a warning, or a countermeasure to break up the water layer.
The antihydroplaning system according to the invention includes, for example, measuring devices to detect vibration of the chassis. Advantageously, these are acoustic sensors, which are mounted preferably on an axle (front axle) of the vehicle. Such sensors aid (for example, by means of a frequency analyzer), in rapidly recognizing the difference between the vibration action on a dry road and in the case of hydroplaning. In addition, the antihydroplaning system according to the invention also has an acoustic sensor for vibration of the vehicle body, which detects the splashing-up of water from a wet road.
The slip of the wheels when the road surface is wet is recognized by means of the rotational wheel speed sensors of the vehicle. When hydroplaning occurs, particularly during breaking, this technique results in rapid recognition of the danger because, in this driving condition, the low coefficient of friction results in an immediate reduction of the rotational speed of the hydroplaning wheels. During acceleration, the reversed slip is similarly a measurement of a dangerous situation. When the vehicle coasts, a hydroplaning effect is also recognized by way of the slip since the hydroplaning wheels are also braked.
Hydroplaning vehicle tires are distinguished by the fact that the curvature of the tire changes in a typical manner at the contact area of the wheel, which phenomenon can also be utilized to detect the occurrence of hydroplaning. Moreover, a distinction with respect to icy patches can be achieved by means of a temperature sensor which measures the temperature of the vehicle surroundings, and thus determines reliably whether it is possible for hydroplaning to occur. (This effect, of course, does not occur below a specific temperature (for example, below 0.degree. C.).
The measures according to invention are not intended primarily for protection against the slipperiness of ice, as to which the inventors have suggested other devices and measures.
By linking the measured values detected by the sensors in a vehicle computer and comparing them with stored vibration curves, the occurrence of a hydroplaning effect is clearly recognized. By means of the output signal of the computer "hydroplaning is occurring", yes or no, or "is within a range with predetermined thresholds", either a warning signal or the following countermeasures can be activated:
Concurrent activation of different above-described countermeasures may also be advantageous.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.